Free cooling cascade arrangement for refrigeration system

Abstract

A refrigeration system includes a medium temperature subsystem circulating a coolant in a closed loop between at least one medium temperature chiller and at least one medium temperature load and at least one cascade heat exchanger, and a low temperature subsystem circulating a coolant in a closed loop between at least one low temperature heat exchanger and at least one low temperature load. A cooling circuit is provided for circulating a coolant and includes a first pump and a second pump and a fluid cooler and a valve, and interfaces with the medium temperature chiller and the low temperature chiller. The valve is movable to a closed position to define a first flow path and a second flow path, where the first flow path includes the first pump and the medium temperature chiller and fluid cooler, and the second flow path including the second pump and the low temperature heat exchanger and the cascade heat exchanger.

What is claimed is: 
     
       1. A refrigeration system, comprising:
 a plurality of medium temperature heat exchangers arranged in parallel and configured to cool a medium temperature coolant for circulation in a first closed loop between the medium temperature heat exchangers and a plurality of medium temperature refrigerated display cases; 
 a plurality of low temperature heat exchangers arranged in parallel and configured to cool a low temperature coolant for circulation in a second closed loop between the low temperature heat exchangers and a plurality of low temperature refrigerated display cases; 
 a condenser coolant supply header configured to supply a condenser coolant to the low and medium temperature heat exchangers; 
 a condenser coolant suction header configured to receive the condenser coolant from the low and medium temperature heat exchangers; 
 a fluid cooler configured to cool the condenser coolant in the condenser coolant supply header; 
 a cascade heat exchanger separate from the medium temperature heat exchangers and arranged in parallel with the medium temperature refrigerated display cases along the first closed loop such that the medium temperature heat exchangers provide a supply of the medium temperature coolant to both the cascade heat exchanger and the medium temperature refrigerated display cases in parallel; 
 at least one first pump configured to pump the condenser coolant from the condenser coolant suction header to the coolant supply header and through the fluid cooler; 
 at least one second pump configured to pump the condenser coolant from the coolant suction header to the condenser coolant supply header and through the cascade heat exchanger; 
 a valve disposed on the condenser coolant supply header between the low temperature heat exchangers and the fluid cooler, the valve movable to a closed position to define a first cooling flow path comprising the first pump and the fluid cooler and the medium temperature heat exchangers, and a second cooling flow path comprising the second pump and the cascade heat exchanger and the low temperature heat exchangers; 
 wherein the cascade heat exchanger is configured to receive both the coolant from the low temperature heat exchangers and the supply of the medium temperature coolant from the medium temperature heat exchangers when the valve is closed and to cool the coolant from the low temperature heat exchangers using the supply of the medium temperature coolant from the medium temperature heat exchangers. 
 
     
     
       2. The refrigeration system of  claim 1  wherein the medium temperature heat exchanger comprises a chiller for cooling a medium temperature liquid coolant circulating to the medium temperature refrigerated display cases. 
     
     
       3. The refrigeration system of  claim 1  wherein the low temperature heat exchanger comprises a chiller for cooling a low temperature liquid coolant circulating to the low temperature refrigerated display cases. 
     
     
       4. The refrigeration system of  claim 3  wherein the low temperature liquid coolant comprises liquid carbon dioxide. 
     
     
       5. The refrigeration system of  claim 1  wherein the low temperature heat exchanger comprises a condenser and the low temperature coolant comprises a refrigerant. 
     
     
       6. The refrigeration system of  claim 5  wherein the refrigerant comprises carbon dioxide or ammonia. 
     
     
       7. The refrigeration system of  claim 1  wherein the first cooling flow path and the second cooling flow path share a common suction header between the first pump and the second pump. 
     
     
       8. The refrigeration system of  claim 7  wherein the valve is movable to an open position to define a third flow path comprising the fluid cooler and the medium temperature heat exchangers and the low temperature heat exchangers. 
     
     
       9. The refrigeration system of  claim 1  wherein the fluid cooler is an outdoor fluid cooler configured to use air at an ambient temperature to cool the coolant. 
     
     
       10. The refrigeration system of  claim 9  further comprising a control system operable to close the valve when the ambient temperature is above a predetermined level, and to open the valve when the ambient temperature is below the predetermined level. 
     
     
       11. The refrigeration system of  claim 8  wherein the second pump is turned on when the valve is in the closed position to circulate the coolant through the second flow path, and the second pump is turned off when the valve is open the open position so that the first pump circulates the coolant through the third flow path. 
     
     
       12. A refrigeration system, comprising:
 at least one medium temperature chiller for cooling a medium temperature coolant circulated in a first closed loop between the medium temperature chiller and at least one medium temperature refrigerated display case; 
 at least one low temperature heat exchanger for cooling a low temperature coolant circulated in a second closed loop between the low temperature heat exchanger and at least one low temperature refrigerated display case; 
 a condenser coolant supply header configured to supply a condenser coolant to the medium temperature chiller and to the low temperature heat exchanger; 
 a condenser coolant suction header configured to receive the condenser coolant from the medium temperature chiller and from the low temperature heat exchanger; 
 a fluid cooler configured to receive and cool the condenser coolant; 
 a cascade heat exchanger separate from the medium temperature chiller and arranged in parallel with the medium temperature refrigerated display case along the first closed loop such that the medium temperature chiller provides a supply of the medium temperature coolant to both the cascade heat exchanger and the medium temperature refrigerated display case in parallel; 
 at least one condenser coolant pump configured to pump the condenser coolant from the condenser coolant suction header to the condenser coolant supply header and through the fluid cooler; 
 at least one cascade pump configured to pump the condenser coolant from the condenser coolant suction header to the condenser coolant supply header and through the cascade heat exchanger; and 
 a valve movable to a closed position to define a first cooling flow path comprising the condenser pump and the fluid cooler and the medium temperature chiller, and a second cooling flow path comprising the cascade pump and the cascade heat exchanger and the low temperature heat exchanger; 
 wherein the cascade heat exchanger is configured to receive both the coolant from the low temperature heat exchanger and the supply of the medium temperature coolant from the medium temperature chiller when the valve is closed and to cool the coolant from the low temperature heat exchanger using the supply of the medium temperature coolant from the medium temperature chiller. 
 
     
     
       13. The refrigeration system of  claim 12  wherein the first cooling flow path and the second cooling flow path share a common suction header between the condenser pump and the cascade pump. 
     
     
       14. The refrigeration system of  claim 13  wherein the valve is movable to an open position to define a third flow path comprising the fluid cooler and the medium temperature chiller and the low temperature heat exchanger. 
     
     
       15. The refrigeration system of  claim 12  wherein the fluid cooler is an outdoor fluid cooler configured to use air at an ambient temperature to cool the coolant. 
     
     
       16. The refrigeration system of  claim 15  further comprising a control system operable to close the valve when the ambient temperature is above a predetermined level, and to open the valve when the ambient temperature is below the predetermined level. 
     
     
       17. The refrigeration system of  claim 14  wherein the cascade pump is turned on when the valve is in the closed position to circulate the coolant through the second flow path, and the second pump is turned off when the valve is open the open position so that the first pump circulates the coolant through the third flow path. 
     
     
       18. A refrigeration system, comprising:
 a medium temperature subsystem circulating a medium temperature coolant in a first closed loop between at least one medium temperature heat exchanger and at least one medium temperature load and at least one cascade heat exchanger separate from the medium temperature heat exchanger and arranged in parallel with the medium temperature load along the first closed loop such that the medium temperature heat exchanger provides the medium temperature coolant to both the cascade heat exchanger and the medium temperature load in parallel; 
 a low temperature subsystem circulating a low temperature coolant in a second closed loop between at least one low temperature heat exchanger and at least one low temperature load; 
 a condenser cooling circuit for circulating a condenser coolant, the condenser cooling circuit having a first pump and a second pump and a fluid cooler and a valve, and interfacing with the medium temperature heat exchanger and the low temperature heat exchanger; 
 wherein the valve is movable to a closed position defining a first flow path and a second flow path, the first flow path including the first pump and the medium temperature heat exchanger and fluid cooler and the second flow path including the second pump and the low temperature heat exchanger and the cascade heat exchanger; 
 wherein the cascade heat exchanger is configured to receive both the coolant from the low temperature heat exchanger and the medium temperature coolant from the medium temperature heat exchanger when the valve is closed and to cool the coolant from the low temperature heat exchanger using the medium temperature coolant from the medium temperature heat exchanger. 
 
     
     
       19. The refrigeration system of  claim 18  wherein the medium temperature heat exchanger comprises a chiller for cooling a medium temperature liquid coolant circulating to the medium temperature load. 
     
     
       20. The refrigeration system of  claim 18  wherein the low temperature heat exchanger comprises a chiller for cooling a low temperature liquid coolant circulating to the low temperature load. 
     
     
       21. The refrigeration system of  claim 20  wherein the low temperature liquid coolant comprises liquid carbon dioxide. 
     
     
       22. The refrigeration system of  claim 18  wherein the low temperature heat exchanger comprises a condenser and the low temperature coolant comprises a refrigerant. 
     
     
       23. The refrigeration system of  claim 22  wherein the refrigerant comprises carbon dioxide or ammonia. 
     
     
       24. The refrigeration system of  claim 18  wherein the valve is movable to an open position to define a third flow path comprising the fluid cooler and the medium temperature heat exchanger and the low temperature heat exchanger. 
     
     
       25. The refrigeration system of  claim 24  further comprising a control system operable to actuate the valve between the open position and the closed position based on a signal representative of an air temperature proximate the fluid cooler. 
     
     
       26. The refrigeration system of  claim 24  wherein the valve is disposed in the cooling circuit between the low temperature chiller and the fluid cooler.